题目

阅读下面材料，根据其内容和所给段落开头语续写两段，使之构成一篇完整短文。An 80-year-old man was sittingon the sofa in his house along withhis 45-year-old son.Suddenly a crow (乌鸦) landed on their window.The father asked hisson, “Whatis this? Theson replied, “This is a crow.Aftera few minutes,the father asked his sonfor the second time, “What is this? The son said, “Father, I told you justnow. It's a crow. After a little while, the father asked his son the samequestion for third time, “What is this? This time, the son was irritated (生气) and sa8．如图是人类遗传病家系谱图，该病的致病基因不可能是（　　）A．Y染色体上的基因B．常染色体上的显性基因C．常染色体上的隐性基因D．X染色体上的显性基因